The invention relates to a cable stranding machine having a plurality of reels supporting the individual filaments to be stranded. Each reel is coupled with an rpm-variable motor for adapting the reel rpm to the stranding speed to determine the tension in the filament as it runs from the reel to the location of stranding. With each reel there is associated a deflecting roller and a compensating roller (filament tension responsive roller) for guiding the filament to be stranded. The compensating roller is carried at the end of a movable support component, such as a compensating arm and with each compensating arm there is connected an arrangement for generating a force (torque) applied to the compensating arm and an arrangement for controlling the rpm of the reel motor.
In cable making, the individual filaments run from respective supply reels, and are directed by guiding elements to the location of stranding where the actual cable forming (stranding) proper takes place. In order to achieve a stranding which yields a high-quality cable, a constant tension must be set and maintained for the individual filaments. In case the filaments to be stranded are not sensitive to tension forces, it is sufficient to appropriately brake the reels of the individual filaments to thus obtain the desired tensioning force.
In case of highly sensitive materials, however, such as glass fiber filaments to be used as optical fibers or copper filaments to be used for making miniature cables, the setting of the tensioning force in the individual filaments by means of a simple braking of the wheel is, for all practical purposes, not possible because the bearing friction in the reel alone generates a tensioning force on the individual filament which is higher than permissible to avoid filament damage. To counteract this effect, the individual reels have to be expediently provided with a four-quadrant electric drive. For controlling the rpm of the reel drive to thus regulate the tensioning force, it is known to have a torque act on the compensating arm by means of a spring. The torque opposes that of the compensating arm, applied thereto by the filament. Further, the compensating arm is coupled with a potentiometer which affects the control of the reel drive motor so that a change in the position of the compensating arm directly varies the rpm of the reel drive motor. By appropriate pre-setting of the spring tension the desired tensioning force may be predetermined in the filament so that the setting torque applied by the spring and the counter torque applied by the tensioning force of the filament are maintained in equilibrium. An excessively high or an excessively low rpm of the reel causes a pivotal motion of the compensating arm and thus changes the setting of the potentiometer. This results in a corresponding change of the rpm of the reel drive motor so that the compensating arm, by means of a torque equilibrium, may assume once again its predetermined initial (basic) position.
It is a particular disadvantage of the above-outlined known apparatus that during a setting motion against the spring force there occurs an increase of the tension force in the filament. Such an increase may lead to damages by stretching the filament should the latter be of a highly sensitive type which allows an exposure to a tensioning force of, for example, not more than 0.5 Newton. The use of springs has a further disadvantage that the change in the tensioning force must also be effected with mechanical means by changing the spring bias. Such a setting, in case of small tolerances, can be effected with the desired accuracy and reproduceability under the given narrow tolerances only with great difficulty, if at all.